Internally generated DFT stepped hysteresis sweep for electrostatic MEMS

ABSTRACT

The present invention generally relates to a mechanism for testing a MEMS hysteresis. A power management circuit may be coupled to the electrodes that cause the movable plate that is disposed between the electrodes in a MEMS device to move. The power management circuit may utilize a charge pump, a comparator and a resistor ladder.

BACKGROUND OF THE DISCLOSURE

Field of the Disclosure

Embodiments of the present disclosure generally relate to a mechanismfor testing a micro-electromechanical system (MEMS) hysteresis.

Description of the Related Art

In operating a MEMS digital variable capacitor (DVC), a plate movesbetween a first position and a second position. The plate moves byapplying a voltage to an actuation electrode. Once the electrode voltagereaches a certain voltage, oftentimes referred to as a snap-in voltage,the plate moves towards the electrode. The plate moves back to theoriginal position once the voltage is lowered to a release voltage. Therelease voltage is typically lower than the snap-in voltage due to thehigher electrostatic forces when the plate is close to the actuationelectrode and due to stiction between the plate and the surface to whichthe plate is in contact once moved closer to the electrode.

Because the plate doesn't release at the same voltage as the snap-involtage, the MEMS DVC has a hysteresis curve. The snap-in voltage andthe release voltage, while different, should be known for the MEMS DVCto operate efficiently.

Therefore, there is a need in the art for a method and device foreffectively measuring the hysteresis curve for a MEMS DVC.

SUMMARY OF THE DISCLOSURE

The present disclosure generally relates to a mechanism for testing aMEMS hysteresis. A power management circuit may be coupled to theelectrodes that cause the movable plate to move between the electrodesin a MEMS device. The power management circuit may utilize a chargepump, a comparator and a resistor ladder.

In one embodiment, a device comprises a first MEMS device having a firstelectrode, a second electrode, and a plate movable between a firstposition spaced a first distance from the first electrode and a secondposition spaced a second distance from the first electrode; a powersource coupled to both the first electrode and the second electrode; anammeter coupled to the first electrode; a voltmeter coupled to both thefirst electrode and the second electrode; a first switch coupled to theplate and to ground; and a second switch coupled to the plate and to apower management circuit.

In another embodiment, a MEMS DVC comprises at least one MEMS device,the MEMS device comprising a movable plate, an RF electrode, one or morepull-down electrodes and one or more pull-up electrodes; a first switchcoupled to either the one or more pull-down electrodes or the one ormore pull-up electrodes, wherein the first switch is additionallycoupled to ground; a second switch coupled to either the one or morepull-down electrodes or the one or more pull-up electrodes; and a powermanagement system coupled to the second switch, wherein the at least oneMEMS device, the first switch, the second switch and the powermanagement system are all disposed on a semiconductor chip.

In another embodiment, a method of testing a MEMS DVC, the MEMS DVCincluding at least one MEMS device, the MEMS device comprising a movableplate, an RF electrode and one or more pull-down electrodes, isdisclosed. The method comprises applying a first voltage to the one ormore pull-down electrodes to move the movable plate from a free standingcapacitance state to an increased capacitance; measuring a capacitanceof the MEMS device; applying a second voltage to the one or morepull-down electrodes; measuring the capacitance of the MEMS device;detecting the capacitance of the MEMS device equals a maximumcapacitance of the MEMS device; removing the second voltage from the oneor more pull-down electrodes; measuring the capacitance of the MEMSdevice; removing the first voltage from the one or more pull-downelectrodes; measuring the capacitance of the MEMS device; and detectingthe capacitance of the MEMS device equals the free standing statecapacitance.

In another embodiment, a method of testing a MEMS DVC, the MEMS DVCincluding at least one MEMS device, the MEMS device comprising a movableplate, an RF electrode and one or more pull-up electrodes, is disclosed.The method comprises applying a first voltage to the one or more pull-upelectrodes to move the movable plate from a free standing capacitancestate to a decreased capacitance; measuring a capacitance of the MEMSdevice; applying a second voltage to the one or more pull-up electrodes;measuring the capacitance of the MEMS device; detecting the capacitanceof the MEMS device equals a minimum capacitance of the MEMS device;removing the second voltage from the one or more pull-up electrodes;measuring the capacitance of the MEMS device; removing the first voltagefrom the one or more pull-up electrodes; measuring the capacitance ofthe MEMS device; and detecting the capacitance of the MEMS device equalsthe free standing state capacitance.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this disclosure and are therefore not to beconsidered limiting of its scope, for the disclosure may admit to otherequally effective embodiments.

FIG. 1 is a schematic cross-sectional illustration of a MEMS DVC devicein the free standing state.

FIG. 2 is a schematic cross-sectional illustration of the MEMS DVCdevice in the C_(max) state.

FIG. 3 is a schematic cross-sectional illustration of the MEMS DVCdevice in the C_(min) state.

FIG. 4 is a schematic illustration of a waveform controller driving theMEMS DVC device.

FIG. 5A is a graph showing the hysteresis curve for an electrostaticallyoperated MEMS device when pulled towards the RF electrode with a voltageapplied to the pull-down electrodes.

FIG. 5B is a graph showing the hysteresis curve for an electrostaticallyoperated MEMS device when pulled away from the RF electrode with avoltage applied to the pull-up electrodes.

FIG. 6 is a schematic illustration of a two terminal MES device CVconfiguration.

FIG. 7 is a schematic illustration of a three terminal MEMS device CVconfiguration.

FIGS. 8A and 8B are schematic illustrations of a DFT implementation totest a MEMS hysteresis according to one embodiment.

FIG. 9 is a schematic illustration of a power management implementationfor MEMS hysteresis testing according to one embodiment.

FIG. 10 is a schematic illustration of test methodology for a discretecapacitance hysteresis test using an internal DFT according to oneembodiment.

FIGS. 11A-11C are schematic illustrations of a DFT implementation totest a MEMS hysteresis according to additional embodiments.

FIGS. 12A and 12B are a flow chart illustrating a method of testing aMEMS DVC according to one embodiment.

FIG. 13A is a schematic cross-sectional illustration of a MEMS DVCdevice having a MIM capacitor in the free standing state.

FIG. 13B is a schematic cross-sectional illustration of the MEMS DVCdevice of FIG. 13A in the C_(max) state.

FIG. 13C is a schematic cross-sectional illustration of the MEMS DVCdevice of FIG. 13A in the C_(min) state.

FIG. 13D is a schematic cross-sectional close up illustration of theMEMS DVC shown in FIG. 13A.

FIG. 13E is a schematic cross-sectional close up illustration of theMEMS DVC shown in FIG. 13B.

FIG. 14 is a schematic cross-sectional illustration of a MEMS DVC deviceaccording to another embodiment.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in oneembodiment may be beneficially utilized on other embodiments withoutspecific recitation.

DETAILED DESCRIPTION

The present disclosure generally relates to a mechanism for testing aMEMS hysteresis. A power management circuit may be coupled to theelectrodes that cause the movable plate that is disposed between theelectrodes to move in a MEMS device. The power management circuit mayutilize a charge pump, a comparator and a resistor ladder.

A MEMS DVC device may operate with electrostatic forces. As discussedherein, the mechanism operated by a force acting on the moveable MEMSelement when a voltage V is applied between the movable MEMS element(e.g., movable plate) and a control electrode. This electrostatic forcescales with (V/gap)². The mechanical counter-balance force comes from aspring suspension system and typically scales linearly with thedisplacement. The result is that with an increasing voltage V the MEMSdevice moves a certain distance δ toward the control-electrode. Thismovement reduces the gap between the movable MEMS element (oftentimesreferred to as a moveable plate) and the electrode, which in turnincreases the electrostatic force further. For small voltages, anequilibrium position between the initial position and the electrode isfound. However, when the voltage exceeds a certain threshold level (thepull-in voltage), the device displacement is such that the electrostaticforce rises faster than the mechanical counterbalance force and thedevice rapidly snaps-in towards the control-electrode until it comes incontact.

The MEMS DVC device may have a control-electrode above (PU-electrode)and below (PD-electrode) the moveable MEMS element, as shownschematically in FIG. 1. In addition an RF-electrode may be presentbelow the moveable MEMS element. As shown in FIGS. 1-3, thePU-electrode, the PD-electrode and the RF electrode are all covered withdielectric material. During operation the MEMS element is eitherpulled-up or pulled-down in contact with the dielectric material toprovide a stable minimum or maximum capacitance to the RF-electrode. Inthis way the capacitance from the moveable element to the RF-electrode(which resides below the moveable element) can be varied from a highcapacitance C_(max) when pulled to the bottom (See FIG. 2) to a lowcapacitance C_(min) (See FIG. 3) when pulled to the top. The voltagesapplied to the PD-electrode (Vbottom) and to the top-electrode (Vtop)are typically controlled by a waveform controller (See FIG. 4) to ensurea long-life stable performance of the DVC device. The moveable elementis typically on DC-ground.

As shown in FIG. 1-3, the MEMS DVC device may comprise a movable platedisposed in a cavity. The movable plate is coupled to ground and movesbetween a free standing state shown in FIG. 1 to a C_(max) state shownin FIG. 2 and a C_(min) state shown in FIG. 3, A voltage may be appliedto one or more pull-in or pull-down electrodes to pull the plate intoclose proximity of the RF electrode. The electrodes are covered by adielectric material. A pull up or pull off electrode may be disposedopposite the pull-in electrodes.

FIG. 5A shows a typical response of the MEMS DVC device to an appliedcontrol voltage to the PD-electrode. Initially, the device is in thefree-standing state as in FIG. 1 and has a capacitance C_(free). As thevoltage on the bottom control electrode is ramped up, the capacitanceslowly increases as the movable plate slowly moves closer to the RFelectrode until the snap-in point p1 is reached at a voltage Vpi(pull-in voltage). At this point the device (i.e., movable plate)quickly snaps in and the capacitance goes to its maximum value C_(max).Because the gap between the MEMS element and the PD-electrode is nowmuch smaller, the electrostatic force has increased and the voltage hasto be reduced down to Vrl (release voltage) in order for the MEMS deviceto release from the bottom at point p2. The capacitance of the MEMSdevice is at the maximum value when the MEMS element is in contact withthe dielectric material that is disposed on the RF electrode.

FIG. 5B shows a typical response of the MEMS DVC device to an appliedcontrol voltage to the PU-electrode. Initially, the device is in thefree-standing state as in FIG. 1 and has a capacitance C_(free). As thevoltage on the top control electrode is ramped up, the capacitanceslowly decreases as the movable plate slowly moves away from the RFelectrode until the snap-in point p3 is reached at a voltage Vpu(pull-up voltage). At this point the device (i.e., movable plate)quickly snaps in and the capacitance goes to its minimum value C_(min).Because the gap between the MEMS element and the PU-electrode is nowmuch smaller, the electrostatic force has increased and the voltage hasto be reduced down to Vrlu (release voltage) in order for the MEMSdevice to release from the top at point p4. The capacitance of the MEMSdevice is at the minimum value when the MEMS element is in contact withthe dielectric material that is disposed on the PU electrode.

The Vpi, Vpu, Vrl and Vrlu are important parameters for the MEMS DVCdevice. If the pull-in voltage Vpi or Vpu is too high then the waveformcontroller may not be able to pull the MEMS devices into contactintimately, which can impact the obtainable C_(min) (upward actuation)or C_(max) (downward actuation). If the release voltage Vrl or Vrlu istoo low this could indicate stiction which impedes proper deviceoperation. Also, if the release voltage Vrl from the bottom is too lowthen this will impede the device to be released from the RF-electrode inthe presence of an RF signal.

Both Vpi, Vpu, Vrl and Vrlu depend on material parameters (Young'sModulus) as well as geometrical parameters, such as layer thicknessesand CD-control of various layers. Therefore, in production, the MEMSdevices will exhibit a certain distribution in these voltages. In orderto screen functional devices that meet all required product specs, it iskey to test the Vpi, Vpu, Vrl and Vrlu on every device. As discussedherein, a built-in test methodology can be used facilitate the test.

The built-in test methodology is termed as “hysteresis testing.”Hysteresis, because the pull-in and release voltages are separated orthe pull-in and the release curves do not overlap as shown in FIGS. 5Aand 5B. For a reliable part (MEMS DVC) Vpi, Vpu, Vii and Vrlu aredesigned to be in a certain range. Otherwise they can result in nonperformance as explained in above paragraphs. Unlike, C_(max) andC_(min), Vpi, Vpu, Vrl and Vrlu are not product specs, i.e. they are notlisted on a product sheet but they are the best gauges for estimatingthe reliability or robustness of the part. Due to process variations,certain parts on a wafer or across the lot may fall outside the rangeand, if escape screening, can lead to failures in the field. Sohysteresis testing allows for screening the bad parts from good.

A typical method for performing a hysteresis test on an electrostaticMEMS device is to perform a CV (capacitance-voltage) sweep. A typical CVsweep can be performed using a CV meter, which uses a combination of aDC source and an AC source to provide the DC bias and the AC signal. Themeasurements are performed by a combination of an AC voltmeter and an ACammeter. The basic test configuration to perform a test on a twoterminal electrostatic MEMS device is shown in FIG. 6.

The MEMS device capacitance is given by the equation, where f is thefrequency of the AC voltage source:C _(MEMS) =i _(ac)/2πf*v _(ac)

A three or more terminal electrostatic MEMS device does not allow forthe same straightforward CV test as shown in FIG. 1. The bias electrodeson the MEMS device provide the actuation bias and are separate from thecapacitor electrodes. A CV sweep is performed on this configuration byusing the same configuration as shown in FIG. 1, but also including a DCsource, Vbias, as shown in FIG. 7. The DC source is used in the samemanner as the DC source in FIG. 6.

A semiconductor chip can be composed of one or more MEMS transducers andmonolithically integrated CMOS control and power management circuitry.This allows for the Vbias power supply in FIG. 7 to be generatedinternal to the semiconductor chip and not in an external power supply.This is shown in FIGS. 8A and 8B as a plurality of MEMS transducers eachwith separate switches to the power management. In FIG. 8A, the powermanagement and the MEMS elements are all disposed on a commonsemiconductor chip. In FIG. 8B, the MEMS elements are disposed onsemiconductor chip 1 and the power management is disposed onsemiconductor chip 2. The Vbias voltage is generated in the integratedpower management circuit and passes to the MEMS transducers throughswitch S2. The actuation voltage for the MEMS transducers is controlledthrough the power management, where the level of the output voltage iscontrolled by the digital control bits C<0:n>, as shown in FIGS. 8A and8B. The hysteresis sweep can be performed by changing the digitalcontrol bits in the power management circuit to the desired actuationvoltage. A primary difference between the external power supply versionin FIG. 7 and the internal SFT mode in FIGS. 8A and 8B is that thedigital control bits hold the value at a discrete number of fixed levels(n) instead of a continuous sweep that can be performed by the externalversion.

One representation of a power management circuit that can allow fordiscrete levels of output voltage is a charge pump with a regulator. Inthe simple case in FIG. 9, the charge pump clock is gated by the outputof the comparator. The output voltage of the charge pump is divided bythe resistor ladder and compared to the bandgap voltage reference. Ifthe voltage reference at the resistor ladder is lower than the value ofthe bandgap voltage reference voltage, the charge pump clock is on. Thiscondition will allow the charge pump clock to be toggling and the chargepump voltage will be increasing if the charge generation is greater thanthe output load current. If the voltage reference at the resistor ladderis higher than the value of the bandgap voltage reference, the chargepump clock is off. As shown in FIG. 9, the programming of the voltagelevel is produced by switching in discrete resistors in the resistorladder, effectively changing the voltage on the compare node to producea higher or lower output voltage set point. In this manner, the value ofthe output voltage is programmed by the address bits C<0:n>.

As shown in FIG. 9, the value of Vactuation will be programmed to be aresistor ratio as compared to the Vbandgap voltage as shown by thefollowing equation for a programmation of c<0>:Vactuation=((Rs+R0)/R0)*Vbandgap

The value for Vactuation with a c<1> programmation is:Vactuation=((Rs+R0+R1)/(R0+R1))*Vbandgap

The value for Vactuation with a c<n> programmation is:Vactuation=((Rs+R0−R1+R2 . . . +Rn)/(R0+R1+R2+ . . . Rn)*Vbandgap

For a discrete hysteresis curve using this OFT method, the test methodconsists of a voltage programmation using the C address bits, a waittime for settling, and a measurement strobe of the capacitance.

The test is implemented in the hardware configuration shown in FIG. 10.The device under test, or DUT, is preset using the address bits to theregulator to output a voltage level to the MEMS that is lower than theVpi. After the DUT is powered up, a wait time, or Tw, for voltage andMEMS settling is implemented in the test sequence before the capacitancelevel is measured by the CV meter at time Ts. After the capacitance ismeasured, the address bits are incremented to the next voltage level andthe measurement is performed using the same timing. Once the Vpi isdetected, the address bits are decremented and the measurements takenuntil the capacitance meter detects ctrl. By utilizing this testsequence, along with the internal DFT, a continuous hysteresis curve canbe represented by discretizing the voltage levels as shown in FIG. 10.

FIGS. 11A and 11B are schematic illustrations of a DFT implementation totest a MEMS hysteresis according to additional embodiments. FIG. 11Ashows an embodiment where the test is performed for voltage applied tothe pull-down electrode 1102 while FIG. 11B shows an embodiment wherethe test is performed for voltage applied to the pull-up electrode 1104.It is contemplated that the test may be performed on both the pull-downelectrode 1102 and pull-up electrode 1104.

The MEMS device 1100 includes the pull-down electrodes 1102, the pull-upelectrode 1104, an RF electrode 1106 and ground electrodes 1108. Theground electrodes 1108 are connected to ground and to the movable plate1110. A dielectric layer 1112 is disposed over the pull-down electrodes1102 and the RF electrode 1106. Another dielectric layer 1114 isdisposed between the pull-up electrode 1104 and the cavity 1116 withinwhich the movable plate 1110 is disposed.

As shown in FIG. 11A, the pull-down electrodes 1102 are coupled tomultiple switches 1118, 1120. The first switch 1118, when engaged,connects the pull-down electrodes 1102 to ground. In FIG. 11B, when thefirst switch 1118 is engaged, the pull-up electrode 1104 is connected toground. The second switch 1120, in FIG. 11A, is connected to a powermanagement device 1122. Similarly, in FIG. 11B, the second switch 1120is connected to the power management device 1122. Thus, when the secondswitch 1120 is engaged, the pull-down electrode 1102 (FIG. 11A) or thepull-up electrode 1104 (FIG. 11B) is connected to the power managementdevice 1122. The power management device 1122 and the MEMS device 1100are both disposed in a single package represented by box 1124. It is tobe understood that the power management device 1122 and the MEMS device1100 are disposed in a single package. In one embodiment, the singlepackage may comprise a single chip having both the power managementdevice 1122 and MEMS device 1100 disposed thereon. In anotherembodiment, the single package may comprise separate chips that operatecollectively as a single entity wherein the MEMS device 1100 is on afirst chip and the power management device 1122 is disposed on a secondchip.

The power management device 1122 includes a charge pump 1128 that iscoupled to a gate 1130. The gate 1130 is coupled to both the Vclock nodeand the output from a comparator 1132. The comparator has inputs fromthe Vbandgap node and the resistive ladder. The resistive ladder is whatdivides the output of the charge pump 1128. The resistive ladderincludes a plurality of resistors R0 . . . Rn which are coupled togetherin series. The address bits c<0>, c<1>, c<n> are programmed toincrementally “actuate” or operate such that the next voltage level isachieved and the capacitance of the MEMS device 1100 is measured. Hence,an incremental voltage is applied by operating the address bits c<0>,c<1>, c<n>. Based upon the incremental voltage increase, the actuationvoltage Vpi to the pull-in electrode (for FIG. 11A) or the actuationvoltage to the pull-up electrode (for FIG. 11B) is determined.Similarly, by decrementally decreasing the voltage (i.e., operating theaddress bits c<0>, c<1>, c<n>), the capacitance is again measured andthe release voltage Vrl from the bottom electrode (for FIG. 11A) or therelease voltage from the top electrode (for FIG. 11B) is detected. Assuch, the hysteresis curve for the particular MEMS device 1100 isdetermined. It is to be understood that multiple MEMS devices may becoupled to the power management device 1122. The multiple MEMS devicesmay collectively operate as a DVC.

FIG. 11C shows an embodiment with four switches 1118A, 1118B, 1120A,1120B whereby both the pull up-electrode 1104 and the pull-downelectrode 1102 are coupled to the power management device 1122 and toground. The pull-up electrode 1104 is coupled to ground through switch1118A and to the power management device 1122 through switch 1120A, Thepull-down electrodes 1102 are coupled to ground through switch 1118B andto the power management device 1122 through switch 1120B. Duringoperation, when the movable plate 1110 is pulled down by the pull-downelectrodes 1102, switch 1120B is connected to the power managementdevice 1122 and switch 1118B is disengaged from ground. Simultaneously,the pull-up electrode 1104 is grounded whereby switch 1118A is connectedto ground and switch 1120A is disengaged from power management device1122. When the movable plate 1110 is pulled up, the pull-up electrode1104 is coupled to the power management device 1122 by switch 1120Awhich is engaged with the power management device 1122 while switch1118A is decoupled from ground. Simultaneously, pull-down electrodes1102 are coupled to ground through switch 1118B while switch 1120B isdisengaged from power management device 1122.

FIG. 12A is a flow chart 1200 illustrating a method of testing a MEMSDVC according to one embodiment. Initially, a low voltage is applied tothe pull-down electrode in step 1202. The voltage applied to thepull-down electrode is to pull the movable plate closer to the RFelectrode and will result in an increase of the MEMS RF-capacitance.After the voltage has been applied, the capacitance of the MEMS deviceis measured in step 1204. If the capacitance is equal to the maximumcapacitance of the MEMS device, then the pull-in voltage Vpi has beendetermined In step 1208. If the measured capacitance is not equal to themaximum capacitance, then the voltage is incrementally increased in step1202, with the capacitance measured with each incremental voltageincrease in step 1204, until the maximum capacitance is reached and thepull-in voltage has been determined in step 1208.

Once the pull-in voltage Vpi has been determined, the release voltage isdetermined. The release voltage is determined by reducing the voltageapplied to the pull-down electrode in step 1210. The capacitance is thenmeasured in step 1212. If the capacitance is equal to the free-standingcapacitance, then the release voltage has been determined. If, however,the measured capacitance is still larger, then the voltage isdecrementally reduced in step 1210. The capacitance is measured for eachdecremental voltage reduction. If the measured capacitance is equal tothe free-standing capacitance in step 1214, then the release voltage hasbeen determined in step 1216.

FIG. 12B is a similar flow chart 1250 illustrating a method of testing aMEMS DVC according to one embodiment. Initially, a low voltage isapplied to the pull-up electrode in step 1252. The voltage applied tothe pull-up electrode is to pull the movable plate away from the RFelectrode and will result in a decrease of the MEMS RF-capacitance.After the voltage has been applied, the capacitance of the MEMS deviceis measured in step 1254. If the capacitance is equal to the minimumcapacitance of the MEMS device, then the pull-up voltage Vpu has beendetermined in step 1258. If the measured capacitance is not equal to theminimum capacitance, then the voltage is incrementally increased in step1252, with the capacitance measured with each incremental voltageincrease in step 1254, until the minimum capacitance is reached and thepull-up voltage has been determined in step 1258.

Once the pull-up voltage Vpu has been determined, the release voltage isdetermined. The release voltage is determined by reducing the voltageapplied to the pull-up electrode in step 1260. The capacitance is thenmeasured in step 1262. If the capacitance is equal to the free-standingcapacitance, then the release voltage has been determined. If, however,the measured capacitance is still larger, then the voltage isdecrementally reduced in step 1260. The capacitance is measured for eachdecremental voltage reduction. If the measured capacitance is equal tothe free-standing capacitance in step 1264, then the release voltage hasbeen determined in step 1266.

It is to be understood that the embodiments disclosed herein are notlimited to the MEMS DVC using the MEMS such as shown in FIG. 1-3. Theembodiments disclosed herein are applicable to MEMS DVC using MIMcapacitors in the MEMS device. FIGS. 13A-13C show a MEMS device using aMIM capacitor that is applicable to the embodiments discussed herein.

FIG. 13A is a schematic cross-sectional illustration of a MEMS DVCdevice 1300 having a MIM capacitor in the free standing state. FIG. 13Bis a schematic cross-sectional illustration of the MEMS DVC device 1300of FIG. 13A in the C_(max) state. FIG. 13C is a schematiccross-sectional illustration of the MEMS DVC device 1300 of FIG. 13A inthe C_(min) state. The MEMS DVC device 1300 includes pull-in electrodes1302, 1304 and an RF line 1306. The RF line 1306 extends throughout thecavity of the MEMS DVC and is common to one or more MEMS devices withinthe cavity. The MEMS bridge includes a layer 1308 that lands on bumps1310 that overlie the pull-in electrodes 1302, 1304. The top layer 1312of the MEMS bridge is connected to the bottom layer 1308 by one or moreposts 1314. The layers 1308, 1312 and posts 1314 comprise a conductivematerial. The top layer 1312 may not extend all the way to the ends ofthe structure, making layer 1312 shorter in length than layer 1308. Thegrounded MEMS bridge is connected to the underlying metallization thoughvia 1316. An insulating layer 1318 is capped with metal electrode 1320which is used to pull the MEMS bridge up to the roof for the C_(min)state. This helps reduce the capacitance of the switch in the C_(min)state. A top insulating layer 1322 which fills the etch holes used toremove the sacrificial layers. The top insulating layer 1322 entersthese holes and helps support the ends of the cantilevers, while alsosealing the cavity so that there is a low pressure environment in thecavities.

To form the MIM, landing posts 1324 are present that are conductive andmake contact with the conducting underside of the MEMS bridge. A surfacematerial, such as a metal feature 1326 is disposed on the conductingpost 1324 that provides good conductivity, low reactivity to the ambientmaterials and high melting temperature and hardness for long lifetime.The underside of the MEMS bridge may be coated with an insulator but awindow is opened on the underside of the MEMS bridge to provide aconducting region 1328 for the conducting post 1324 to make electricalcontact with when the MEMS bridge is pulled down. A dielectric layer1330 is formed over the pull-in electrodes 1302, 1304, but not the RFline 1306.

FIG. 13B shows the MEMS bridge pulled in with voltages applied topull-in electrodes 1302, 1304 so that the layer 1308 lands on theinsulated bumps 1310. The conducting region 1328 of the MEMS bridgelands on the two conducting post 1324 (only one shown as the other isbehind it), which gives the low resistance state. FIG. 13C shows theMEMS bridge after it has been pulled to the roof using electrode 1320.The MEMS bridge makes contact with the insulating layer 1318. Thisprevents any electrical contact between the pull up electrode 1320 andthe MEMS bridge. The region in the dotted rectangles is shown in FIGS.13D and 13E.

Although not shown in these figures, there may be an insulating layerover the top and most of the underside of the MEMS bridge. A hole ismade in the insulator on the underside of the cantilever to allow it tomake contact with the conducting post 1324. In this state the resistanceof the MEMS bridge to the RF line is very large and the capacitancecoupling to that line is small.

The embodiments discussed herein are also applicable to hybrid ohmic-MIMdevices, FIG. 14 is a schematic cross-sectional illustration of a MEMSDVC device 1400 according to another embodiment. In the embodiment shownin FIG. 14, a surface material, such as a metal feature 1402 is disposedon the conducting post 1324 that provides good conductivity, lowreactivity to the ambient materials and high melting temperature andhardness for long lifetime. The dielectric layer 1330 that covered onlythe pull-in electrodes 1302, 1304 is replaced with a dielectric layer1404 that is deposited on top of pull in electrodes 1302, 1304 and ontop of RF line 1306, The metal feature 1326, the dielectric layer 1404and the RF line 1306 implement a MIM capacitor. The top electrode ofthis MIM is either electrically floating, when the MEMS bridge is in UPposition, or grounded via the ohmic contact between surface material1402 and conducting region 1328, when the MEMS bridge is in DOWNposition.

In an alternative embodiment, the metal feature 1402, 1326, which is thetop electrode of the MIM, is electrically connected to a reference DCpotential by a variable resistor. The reference DC potential can beeither the common ground, or a separate terminal of the device. Thevariable resistor can be implemented, as an example implementation, by atransistor or a separate higher resistance MEMS ohmic switch.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

The invention claimed is:
 1. A MEMS DVC, comprising: at least one MEMSdevice, the MEMS device comprising a movable plate, an RF electrode, oneor more pull-down electrodes and one or more pull-up electrodes; a firstswitch coupled to either the one or more pull-down electrodes of theMEMS device or the one or more pull-up electrodes of the MEMS device,wherein the first switch is additionally coupled to ground; a secondswitch coupled to either the one or more pull-down electrodes of theMEMS device or the one or more pull-up electrodes of the MEMS device;and a power management system coupled to the second switch, wherein theat least one MEMS device, the first switch, the second switch and thepower management system are all disposed in a single package.
 2. TheMEMS DVC of claim 1, wherein the single package comprises a firstsemiconductor chip having the power management system disposed thereonand a second semiconductor chip having the MEMS device disposed thereon.3. The MEMS DVC of claim 1, wherein the power management systemcomprises: a charge pump; and a resistive ladder coupled between thecharge pump and the second switch.
 4. The MEMS DVC of claim 3, whereinthe power management system further comprises a comparator coupledbetween the charge pump and the resistive ladder.
 5. The MEMS DVC ofclaim 4, wherein the power management system further comprises a gatecoupled between the comparator and the charge pump.
 6. The MEMS DVC ofclaim 5, wherein the comparator is coupled to a bandgap voltage node onthe semiconductor chip.
 7. The MEMS DVC of claim 6, wherein the gate iscoupled to a clock voltage node on the semiconductor chip.
 8. The MEMSDVC of claim 7, wherein the resistive ladder comprises a plurality ofresistors.
 9. The MEMS DVC of claim 8, further comprising a plurality ofaddress bits coupled to the resistive ladder.
 10. The MEMS DVC of claim9, wherein the second switch is coupled to the one or more pull-downelectrodes.
 11. The MEMS DVC of claim 9, wherein the second switch iscoupled to the one or more pull-up electrodes.
 12. The MEMS DVC of claim1, wherein the second switch is coupled to the one or more pull-downelectrodes.
 13. The MEMS DVC of claim 1, wherein the second switch iscoupled to the one or more pull-up electrodes.
 14. The MEMS DVC of claim1, wherein the power management system includes a resistive ladderhaving a plurality of resistors.
 15. The MEMS DVC of claim 14, whereinthe resistive ladder is coupled to one or more address bits.
 16. TheMEMS DVC of claim 15, wherein the plurality of resistors are coupledtogether in series.
 17. The MEMS DVC of claim 1, wherein the firstswitch is coupled to the one or more pull-down electrodes and the secondswitch is coupled to the one or more pull-down electrodes, the MEMS DVCfurther comprising: a third switch coupled to the one or more pull-upelectrodes and to ground; and a fourth switch coupled to the one or morepull-up electrodes and to the power management system.
 18. The MEMS DVCof claim 17, wherein the power management system includes a resistiveladder having a plurality of resistors.
 19. The MEMS DVC of claim 18,wherein the resistive ladder is coupled to one or more address bits. 20.The MEMS DVC of claim 1, wherein the MEMS DVC includes a MIM capacitor.21. A method of testing the MEMS DVC of claim 1, the method comprising:applying a first voltage to the one or more pull-down electrodes of theMEMS device to move the movable plate from a free standing statecapacitance to an increased capacitance state; measuring a capacitanceof the MEMS device; applying a second voltage to the one or morepull-down electrodes of the MEMS device; measuring the capacitance ofthe MEMS device; detecting the capacitance of the MEMS device equals amaximum capacitance of the MEMS device; removing the second voltage fromthe one or more pull-down electrodes of the MEMS device; measuring thecapacitance of the MEMS device; removing the first voltage from the oneor more pull-down electrodes of the MEMS device; measuring thecapacitance of the MEMS device; and detecting the capacitance of theMEMS device is equal to the free standing state capacitance.
 22. Amethod of testing the MEMS DVC of claim 1, the method comprising:applying a first voltage to the one or more pull-up electrodes of theMEMS device to move the movable plate from a free standing statecapacitance to a decreased capacitance state; measuring a capacitance ofthe MEMS device; applying a second voltage to the one or more pull-upelectrodes of the MEMS device; measuring the capacitance of the MEMSdevice; detecting the capacitance of the MEMS device equals a minimumcapacitance of the MEMS device; removing the second voltage from the oneor more pull-up electrodes of the MEMS device; measuring the capacitanceof the MEMS device; removing the first voltage from the one or morepull-up electrodes of the MEMS device; measuring the capacitance of theMEMS device; and detecting the capacitance of the MEMS device is equalto the free standing state capacitance.